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Mössbauer spectrum of 57Co: CoF3
NORG.
NUCL.
CHEM.
LETTERS
Vol.
5,
pp.
16"~-167. 1969.
Pergamon
MOSSBAUER SPECTRUM OF J.M. Friedt and J.P.
Pr.ss.
Printed
In
Great
Britain
57Co: C o F 3
Adloff
C e n t r e de R e c h e r c h e s N u c l @ a i r e s 9 D@partement de C h i m i e N u c l ~ a i r e Rue du L o e s s , S t r a s b o u r g 3~ France
67,
{Received I Novernbee 1968)
R e c e n t i n v e s t i g a t i o n s h a v e s h o w n c o n s i d e r a b l e i n t e r e s t in the M S s s b a u e r s t u d i e s of the a f t e r e f f e c t s of 57Co E . C . a n d m o l e c u l a r c o n s e q u e n c e s of E . C .
in s o l i d c o m p o u n d s (1). The a t o m i c
a n d the s u b s e q u e n t A u g e r c a s c a d e h a v e
b e e n b e a u t i f u l l y d e m o n s t r a t e d in t h e g a s e o u s p h a s e . The s i t u a t i o n i s s t i l l v e r y c o n f u s i n g in the s o l i d s t a t e w h e r e n e u t r a l i s a t i o n of h i g h e r c h a r g e s t a t e s is much f a s t e r .
The e x i s t e n c e of s e v e r a l v a l e n c e s t a t e s of 5 7 F e in 5 7 C o - d o p e d
h o s t s , o r in s t o i c h i o m e t r i c c o m p o u n d s of the l a b e l l e d e l e m e n t , h a s b e e n c l a i m e d on s e v e r a l o c c a s i o n s .
S i n c e the c o n v i n c i n g e x p e r i m e n t d e s c r i b e d b y
T r i f t s h N u s e r a n d C r a i g (2), it m u s t be a d m i t t e d t h a t c h a r g e s t a t e s d e t e c t e d b y M~Sssbauer s p e c t r o s c o p y a r e s t a b l e on a time s c a l e c o m p a r a b l e to the l i f e t i m e of the n u c l e a r l e v e l ( 1 0 - 7 s ) . The q u e s t i o n now r e m a i n s w h a t k i n d of s t r u c t u r a l , c h e m i c a l o r p h y s i c a l p a r a m e t e r s i n t e r f e r e to d e t e r m i n e the s t a t e of the d a u g h t e r atom of
57Co.
If the v a l e n c y of the p a r e n t h a s a d e t e r m i n a t i v e r o l e ~ the s e a r c h of h i g h - c h a r ged i r o n s p e c i e s s h o u l d be m o r e p r o m i s i n g s t a r t i n g with a Co 3+ c o m p o u n d . In a t h e o r e t i c a l a p p r o a c h , P o l l a k (3) p r e d i c t s an a p p r e c i a b l e amount of F e n+ (n = 4, 5 and 6) i m m e d i a t e l y a f t e r the n u c l e a r d e c a y . We h a v e m e a s u r e d the M ~ s s b a u e r s p e c t r u m of 5 7 C o - l a b e l l e d C o F 3 ( c o b a l t i c f l u o r i d e i s one of the v e r y few s i m p l e i o n i c s p e c i e s of Co 3+) a g a i n s t a m o v a b l e s i n g l e - l i n e a b s o r b e r of e n r i c h e d Na4Fe(CN)6,10H20.
C o F 3 b e l o n g s to the R~C s p a c e g r o u p with a b i m o l e c u l a r
r h o m b i c u n i t c e l l (4). E a c h Co i s s u r r o u n d e d b y s i x F - f o r m i n g a n e a r l y r e g u l a r o c t a h e d r o n a n d the six n e i g h b o u r i n g Co a t o m s a r e e q u i v a l e n t . A l l Co s i t e s a r e 163
164
SPECTRUM OF 57Co: CoF 3
Vol. 5. No.3.
l o c a t e d on C 3 a x e s . The a n t i f e r r o m a g n e t i s m of C o F 3 h a s b e e n s t u d i e d b y n e u t r o n d i f f r a c t i o n ; the Neel t e m p e r a t u r e is /450 °K(5). The m a g n e t o c h e m i c a l i n v e s t i g a t i o n (6) did not c o n f i r m this c h a r a c t e r and the m e a s u r e d m a g n e t i c moment (2.1 ~B at 20 °C) lies well b e h i n d the e x p e c t e d v a l u e ( 5 . 3 ~B ). The M 6 s s b a u e r s p e c t r u m of the c o r r e s p o n d i n g i r o n compound F e F 3 has b e e n d e s c r i b e d b y s e v e r a l a u t h o r s (7) . C o F 3 has b e e n p r e p a r e d b y f l u o r i n a t i o n of a n h y d r o u s 57Co :CoC12 at/+50 °C. All h a n d l i n g s of the p r o d u c t have to be a c h i e v e d in i n e r t and d r y a t m o s p h e r e s to a v o i d the d e c o m p o s i t i o n of the v e r y m o i s t u r e s e n s i t i v e f l u o r i d e ; the M ~ s s b a u e r s o u r c e is e n c l o s e d in tight c o p p e r c a p s u l e s with Be o r teflon w i n d o w s . The compound has b e e n c h e c k e d b y X r a y d i f f r a c t i o n , c h e m i c a l and m a g n e t i c a n a l y s e s . T y p i c a l s p e c t r a a r e p r e s e n t e d on f i g u r e 1 and the d e r i v e d p a r a m e t e r s a r e g i v e n in the table b e l o w : T°K
I.S. m m
s -I
Q.S.
mm
s -I
Hin t kG
94
0 . 6 7 ~- 0 . 0 3
0.o5
613 ± 5
294.5
0 . 5 8 -~ 0 . 0 3
0.05
489 ± 6
358
0 . 5 3 ~- 0 . 0 3
0.05
621+5
460
o . 4 3 + o .05
The a b s o r b e r is at r o o m t e m p e r a t u r e . The q u o t e d e r r o r s c o r r e s p o n d to e x p e r i m e n t a l d e v i a t i o n s . The p r o m i n e n t f a c t is that 5 7 F e e x i s t s only in the F e 3+ s t a t e as is r e v e a l e d by the i s o m e r i c shift and the Hin t v a l u e s . T h e s e r e s u l t s a r e p a r t I y i n c o n s i s t e n t with own e a r l i e r s p e c t r a (8) in w h i c h l i n e s w e r e a s c r i b e d to the p r e s e n c e of F e 2+ and w e r e a c t u a l l y due to d e c o m p o s i t i o n p r o d u c t s of C o F 3 ( f i g . 2 ) (these impurities are tentatively
a s c r i b e d f r o m t h e i r M ~ s s b a u e r s p e c t r a to
C o F 2 and an o x i f l u o r i d e of Co 3+). T h e y a p p e a r i n e v i t a b l y in the s p e c t r a of 5 7 F e - d o p e d C o F 3 and r e s u l t from t r a c e s of i r o n h y d r o x i d e f o r m e d d u r i n g the s y n t h e s i s of CoC12 which is the f i r s t step in the p r e p a r a t i o n of C o F 3 .
Vol. 5, Ho. 3.
SPECTRUM OF 57Coe CoPS
165
Cm0 a l
j
*,,
4, ..%
:.~'~:.. ,:.:
f "".,a: "& *it
:
"
.:
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tm
:./:
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:
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D
., •
.
:
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..
• to I
~'~%.
:i~.
:
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2"
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:. ;
~."
"::"
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.
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FIG. 1 M ~ s s b a u e r s p e c t r a of 5 7 C o : C o F 3 at 96 °K ( u p p e r f i g u r e ) and 2 9 6 . 5 • K No q u a d r u p o l e splitting is r e v e a l e d within the limit of the r e s o l u t i o n of the s p e c t r o m e t e r . At l i q u i d n i t r o g e n t e m p e r a t u r e the Q . S .
is l e s s than 0 . 0 5 nun s -1
w h i c h is n o r m a l f o r a high spin F e 3+ in a n e a r l y p e r f e c t o c t a h e d r a l e n v i r o n m e n t . The I . S .
v a l u e c a l c u l a t e d a g a i n s t the s t a n d a r d n i t r o p r u s s i d e a b s o r b e r at 295°K is
0 . 7 8 mm s - 1 . The v a l u e of the i n t e r n a l m a g n e t i c f i e l d Hin t is c h a r a c t e r i s t i c of a 6S F e 3+ i o n . The d i p o l a r c o n t r i b u t i o n to Hin t is n e g l i g i b l e in the c a s e of a vanishing Q . S . and the main part of Hin t is due to the Fermi contact term. The zero-value of Hin t could not be ascertained but the relative values of Hin t in F e F 3 and COF3(9) confirm the highly ionic character of C o F 3 well in line with the measured I. S .(I0). A Neel temperature of 460 ± i .5 °K is deduced from the
166
SPECTRUM OF
CIilll
57¢o, CoF3
i
¥ol. 5, Ho. 3.
i
I|| I
i
FI I"
Fes • ....
- ~:
'
..'.
• ~ :,, :':,: ,',-"i ;:2
:~: .,:
. . ... . .~',. . •
N
l
-. :. ¢ -" •:
:
/ :':
.~.
."
, ~i -~,
: ?
. .'
.: ..- :,
,
•..
"~
: -; -. -: -: -:
-: :
:
;
;
l : ; ..h
FIG. 2 M ~ s s b a u e r spectrum at 9/+ °K of partially decomposed 5 7 C o : C o F 3
speclra, in good accordance with the neutron diffraction experiment, if one takes into account the increased instability of the compound at high temperatures. The observation of solely the F e 3+ charge state is interesting. F r o m simple charge compensation arguments, one deduces that the stable charge state of 57Fe should be identical to the state of the parent atom. That this is realized shows that all electronic aftereffects of the A u g e r cascade in C o F 3 are extinguished in a time shorter than the nuclear lifetime. References I. H . H . W l C K M A N
and G . K . % V E R T H E I M ,
bauer Spectroscopy" (V.I. G O L D A N S K I I
in "Chemical Applications of M ~ s s and R . H . H E R B E R
editors), Aca-
demic Press, N e w Y o r k (1968) p.548. 2. W . T R I F T S H A U S E R 3. H. P O L L A K ,
Phys.Rev.162,
274 (1967).
Phys.Stat. Sol. 2, 720 (1962);
G.K. %VERTHEIM 4. M . A .
and P. C R A I G ,
and H.J. G U G G E N H E I M ,
HEPWORTH,
].Chem.Phys./+2, 3873 (1965).
K.H. JACK, R.D. PEACOCK
and G.J. W E S T L A N D ,
Acta Cryst.10, 63 (1957). 5. E . O . % V O L L A N , Phys.Rev.ll2, 6. P. H E U K E L R.S. NYHOLM
H.R. CHILD,
%V.C. K O E H L E R
and M . K .
WILKINSON,
1132 (1958).
and W . K L E M M ,
Zeit.Anorg.Allg.Chem.222,
and A . G . S H A R P E ,
J.Chem.Soc.,
73 (1935);
3579 (1952).
VM. 5, No. 3.
SPECTRUM OF 57Cos CoF3
167
7. U. BERTHELSEN, ].M. KNUDSEN and H. KROGH, Phys.Stat.Sol.22, 59 (1967); G.K. W E R T H E I M , H.J. G U G G E N H E I M and D.N. B U C H A N A N , Phys.Rev. 169, /+65(1968). 8. ].M. FRIEDT, ].P. A D L O F F , ComptoRend.Acad.Sc.246 C, 1356 (1967). 9. R.E. W A T S O N
and A.]. F R E E M A N , Phys.Rev.123, 2027 (1961).
i0. L.R. W A L K E R , G.K. W E R T H E I M 98 (1961).
and V. ]ACCARINO, Phys.Rev.Lett.6,
NUCL.
CHEM.
LETTERS
Vol.
5,
pp.
16"~-167. 1969.
Pergamon
MOSSBAUER SPECTRUM OF J.M. Friedt and J.P.
Pr.ss.
Printed
In
Great
Britain
57Co: C o F 3
Adloff
C e n t r e de R e c h e r c h e s N u c l @ a i r e s 9 D@partement de C h i m i e N u c l ~ a i r e Rue du L o e s s , S t r a s b o u r g 3~ France
67,
{Received I Novernbee 1968)
R e c e n t i n v e s t i g a t i o n s h a v e s h o w n c o n s i d e r a b l e i n t e r e s t in the M S s s b a u e r s t u d i e s of the a f t e r e f f e c t s of 57Co E . C . a n d m o l e c u l a r c o n s e q u e n c e s of E . C .
in s o l i d c o m p o u n d s (1). The a t o m i c
a n d the s u b s e q u e n t A u g e r c a s c a d e h a v e
b e e n b e a u t i f u l l y d e m o n s t r a t e d in t h e g a s e o u s p h a s e . The s i t u a t i o n i s s t i l l v e r y c o n f u s i n g in the s o l i d s t a t e w h e r e n e u t r a l i s a t i o n of h i g h e r c h a r g e s t a t e s is much f a s t e r .
The e x i s t e n c e of s e v e r a l v a l e n c e s t a t e s of 5 7 F e in 5 7 C o - d o p e d
h o s t s , o r in s t o i c h i o m e t r i c c o m p o u n d s of the l a b e l l e d e l e m e n t , h a s b e e n c l a i m e d on s e v e r a l o c c a s i o n s .
S i n c e the c o n v i n c i n g e x p e r i m e n t d e s c r i b e d b y
T r i f t s h N u s e r a n d C r a i g (2), it m u s t be a d m i t t e d t h a t c h a r g e s t a t e s d e t e c t e d b y M~Sssbauer s p e c t r o s c o p y a r e s t a b l e on a time s c a l e c o m p a r a b l e to the l i f e t i m e of the n u c l e a r l e v e l ( 1 0 - 7 s ) . The q u e s t i o n now r e m a i n s w h a t k i n d of s t r u c t u r a l , c h e m i c a l o r p h y s i c a l p a r a m e t e r s i n t e r f e r e to d e t e r m i n e the s t a t e of the d a u g h t e r atom of
57Co.
If the v a l e n c y of the p a r e n t h a s a d e t e r m i n a t i v e r o l e ~ the s e a r c h of h i g h - c h a r ged i r o n s p e c i e s s h o u l d be m o r e p r o m i s i n g s t a r t i n g with a Co 3+ c o m p o u n d . In a t h e o r e t i c a l a p p r o a c h , P o l l a k (3) p r e d i c t s an a p p r e c i a b l e amount of F e n+ (n = 4, 5 and 6) i m m e d i a t e l y a f t e r the n u c l e a r d e c a y . We h a v e m e a s u r e d the M ~ s s b a u e r s p e c t r u m of 5 7 C o - l a b e l l e d C o F 3 ( c o b a l t i c f l u o r i d e i s one of the v e r y few s i m p l e i o n i c s p e c i e s of Co 3+) a g a i n s t a m o v a b l e s i n g l e - l i n e a b s o r b e r of e n r i c h e d Na4Fe(CN)6,10H20.
C o F 3 b e l o n g s to the R~C s p a c e g r o u p with a b i m o l e c u l a r
r h o m b i c u n i t c e l l (4). E a c h Co i s s u r r o u n d e d b y s i x F - f o r m i n g a n e a r l y r e g u l a r o c t a h e d r o n a n d the six n e i g h b o u r i n g Co a t o m s a r e e q u i v a l e n t . A l l Co s i t e s a r e 163
164
SPECTRUM OF 57Co: CoF 3
Vol. 5. No.3.
l o c a t e d on C 3 a x e s . The a n t i f e r r o m a g n e t i s m of C o F 3 h a s b e e n s t u d i e d b y n e u t r o n d i f f r a c t i o n ; the Neel t e m p e r a t u r e is /450 °K(5). The m a g n e t o c h e m i c a l i n v e s t i g a t i o n (6) did not c o n f i r m this c h a r a c t e r and the m e a s u r e d m a g n e t i c moment (2.1 ~B at 20 °C) lies well b e h i n d the e x p e c t e d v a l u e ( 5 . 3 ~B ). The M 6 s s b a u e r s p e c t r u m of the c o r r e s p o n d i n g i r o n compound F e F 3 has b e e n d e s c r i b e d b y s e v e r a l a u t h o r s (7) . C o F 3 has b e e n p r e p a r e d b y f l u o r i n a t i o n of a n h y d r o u s 57Co :CoC12 at/+50 °C. All h a n d l i n g s of the p r o d u c t have to be a c h i e v e d in i n e r t and d r y a t m o s p h e r e s to a v o i d the d e c o m p o s i t i o n of the v e r y m o i s t u r e s e n s i t i v e f l u o r i d e ; the M ~ s s b a u e r s o u r c e is e n c l o s e d in tight c o p p e r c a p s u l e s with Be o r teflon w i n d o w s . The compound has b e e n c h e c k e d b y X r a y d i f f r a c t i o n , c h e m i c a l and m a g n e t i c a n a l y s e s . T y p i c a l s p e c t r a a r e p r e s e n t e d on f i g u r e 1 and the d e r i v e d p a r a m e t e r s a r e g i v e n in the table b e l o w : T°K
I.S. m m
s -I
Q.S.
mm
s -I
Hin t kG
94
0 . 6 7 ~- 0 . 0 3
0.o5
613 ± 5
294.5
0 . 5 8 -~ 0 . 0 3
0.05
489 ± 6
358
0 . 5 3 ~- 0 . 0 3
0.05
621+5
460
o . 4 3 + o .05
The a b s o r b e r is at r o o m t e m p e r a t u r e . The q u o t e d e r r o r s c o r r e s p o n d to e x p e r i m e n t a l d e v i a t i o n s . The p r o m i n e n t f a c t is that 5 7 F e e x i s t s only in the F e 3+ s t a t e as is r e v e a l e d by the i s o m e r i c shift and the Hin t v a l u e s . T h e s e r e s u l t s a r e p a r t I y i n c o n s i s t e n t with own e a r l i e r s p e c t r a (8) in w h i c h l i n e s w e r e a s c r i b e d to the p r e s e n c e of F e 2+ and w e r e a c t u a l l y due to d e c o m p o s i t i o n p r o d u c t s of C o F 3 ( f i g . 2 ) (these impurities are tentatively
a s c r i b e d f r o m t h e i r M ~ s s b a u e r s p e c t r a to
C o F 2 and an o x i f l u o r i d e of Co 3+). T h e y a p p e a r i n e v i t a b l y in the s p e c t r a of 5 7 F e - d o p e d C o F 3 and r e s u l t from t r a c e s of i r o n h y d r o x i d e f o r m e d d u r i n g the s y n t h e s i s of CoC12 which is the f i r s t step in the p r e p a r a t i o n of C o F 3 .
Vol. 5, Ho. 3.
SPECTRUM OF 57Coe CoPS
165
Cm0 a l
j
*,,
4, ..%
:.~'~:.. ,:.:
f "".,a: "& *it
:
"
.:
.. $
tm
:./:
'.~::
.-
•
..
:
:
:
..:
D
., •
.
:
..
..
• to I
~'~%.
:i~.
:
iN[
2"
!
.~
."
~:.::"-',k.' ,z~.:,
:. ;
~."
"::"
.
"
~,
,
:"
~:':~
/
:
.
•
FIG. 1 M ~ s s b a u e r s p e c t r a of 5 7 C o : C o F 3 at 96 °K ( u p p e r f i g u r e ) and 2 9 6 . 5 • K No q u a d r u p o l e splitting is r e v e a l e d within the limit of the r e s o l u t i o n of the s p e c t r o m e t e r . At l i q u i d n i t r o g e n t e m p e r a t u r e the Q . S .
is l e s s than 0 . 0 5 nun s -1
w h i c h is n o r m a l f o r a high spin F e 3+ in a n e a r l y p e r f e c t o c t a h e d r a l e n v i r o n m e n t . The I . S .
v a l u e c a l c u l a t e d a g a i n s t the s t a n d a r d n i t r o p r u s s i d e a b s o r b e r at 295°K is
0 . 7 8 mm s - 1 . The v a l u e of the i n t e r n a l m a g n e t i c f i e l d Hin t is c h a r a c t e r i s t i c of a 6S F e 3+ i o n . The d i p o l a r c o n t r i b u t i o n to Hin t is n e g l i g i b l e in the c a s e of a vanishing Q . S . and the main part of Hin t is due to the Fermi contact term. The zero-value of Hin t could not be ascertained but the relative values of Hin t in F e F 3 and COF3(9) confirm the highly ionic character of C o F 3 well in line with the measured I. S .(I0). A Neel temperature of 460 ± i .5 °K is deduced from the
166
SPECTRUM OF
CIilll
57¢o, CoF3
i
¥ol. 5, Ho. 3.
i
I|| I
i
FI I"
Fes • ....
- ~:
'
..'.
• ~ :,, :':,: ,',-"i ;:2
:~: .,:
. . ... . .~',. . •
N
l
-. :. ¢ -" •:
:
/ :':
.~.
."
, ~i -~,
: ?
. .'
.: ..- :,
,
•..
"~
: -; -. -: -: -:
-: :
:
;
;
l : ; ..h
FIG. 2 M ~ s s b a u e r spectrum at 9/+ °K of partially decomposed 5 7 C o : C o F 3
speclra, in good accordance with the neutron diffraction experiment, if one takes into account the increased instability of the compound at high temperatures. The observation of solely the F e 3+ charge state is interesting. F r o m simple charge compensation arguments, one deduces that the stable charge state of 57Fe should be identical to the state of the parent atom. That this is realized shows that all electronic aftereffects of the A u g e r cascade in C o F 3 are extinguished in a time shorter than the nuclear lifetime. References I. H . H . W l C K M A N
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